Trip device for an electric circuit breaker having an electromagnetic pump and a time delay means



Aug. 2, 1966 P. KOTOS 3,264,430

TRIP DEVICE FOR AN ELECTRIC cmcum BREAKER HAVING AN ELECTROMAGNETIC PUMP AND A TIME DELAY MEANS Filed Sept. 17, 1964 2 Sheets-Sheet 1 INVENTOR. PETER KoTos,

BY Um 6m ATTORNEY Aug. 2, 1966 v P. KOTO TRIP DEVICE FOR AN ELECTRIC CIRCUIT BREAKER HAVING AN ELECTROMAGNETIC PUMP AND A TIME DELAY MEANS Filed Sept. 1'7, 1964 77/145 //v SECONDS z c A 0. Iowa I I I I I I II 2 Sheets-Sheet 2 I I I //v VEA/TO/F. PETER K0 To 3 5y MMWW United States Patent 3,264,430 TRIP DEVICE FOR AN ELECTRIC CIRCUIT BREAK- ER HAVING AN ELECTROMAGNETIC PUMP AND A TIME DELAY MEANS Peter Kotos, Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York Filed Sept. 17, 1964, Ser. No. 397,206 12 Claims. (Cl. 200-112) This invention relates to a trip device for an electric circuit breaker and, more particularly, relates to a trip device that utilizes an electromagnetic pump for developing a force for tripping the circuit breaker in response to an overcurrent.

For protecting electrical apparatus from the effects of overcurrent, it is customary to provide an overcurrentsensitive protective device that operates to interrupt the overcurrent after a time delay varying inversely with re spect to the magnitude of the current. Quite commonly, it is desired that this time delay vary inversely with respect to the square of the current. This time current characteristic can be expressed mathematically by the following expression: t=K/I where t is the time required for operation once the overcurrent begins, I is the current, and K is a constant.

One way of obtaining this time-current characteristic, and the way that I am particularly concerned with, is to utilize a current sensitive electromagnetic pump for forcing liquid through a conduit into a pressure sensitive actuator that controls the trip latch of a circuit breaker. The electromagnetic pump, which is energized by current that is a direct function of the current in the circuit being protected, is designed to force liquid through the conduit leading to the pressure sensitive actuator at a flow rate that varies directly with the square of the pump energizing current. After the pressure sensitive actuator has received a predetermined net quantity of said liquid from the conduit, it releases the trip latch of the circuit breaker to interrupt the overcurrent.

It is desirable that trip devices such as this be adjustable so that the time required to trip the circuit breaker in response to a given current can be adjusted. This adjustment, however, should not impair the ability of the trip device to respond in accordance with its previouslydecided-upon time current characteristic, which in the assumed case is t=K/I This adjustment also should not change the minimum current level at which the trip device begins to respond (i.e., the pick-up current).

Accordingly, an object of my invention is to provide means for adjusting the response time of an electromagnetic pump type of trip device without appreciably changing its basic time-current characteristic or its pick-up current.

Another object is to provide simple, inexpensive timeadjusting means of this character which readily lends itself to adjustments over a wide range of operating times.

Still another object is to provide time-adjusting means which has a high degree of precision that remains substantially unchanged at all ranges on the time scale.

Another object is to provide adjusting means of this nature which readily lends itself to a sealed system wherein there is no direct communication between the conductive liquid and atmospheric air.

In carrying out my invention in one form, I provide a current-sensitive trip device comprising a conduit containing an electrically conductive liquid and means including an electromagnetic pump for pumping liquid through said conduit at a flow rate varying as a function of the current flowing through an electric circuit. The trip device further comprises a tripping chamber hydraulically connected to the conduit for receiving liquid pumped therethrough and a tripping actuator exposed to the liq- 3,264,430 Patented August 2, 1966 uid in the tripping chamber and movable in a direction to trip the circuit breaker when the pressure in the tripping chamber exceeds a predetermined minimum value. Also connected to the conduit so as to receive liquid forced therethrough by the pump is a timing chamber. Exposed to the liquid in the timing chamber is a timing structure that is movable to increase the volumetric capacity of the timing chaInbe-r when the pressure of the liquid therein exceeds a predetermined minimum value. Motion of the tripping actuator in a tripping direction is opposed by first biasing means and motion of the timing structure in a direction to increase said volume is opposed by second biasing means. The second biasing means permits the timing structure to move at a lower minimum pressure than the minimum pressure required to move the tripping actuator, whereby liquid forced through the conduit causes motion of the timing structure before causing motion of the tripping actuator. Adjustable stop means is provided for blocking motion of the timing structure after a predetermined amount of timing structure motion, thereafter allowing the tripping actuator to move and perform its intended tripping function.

For a better understanding of my invention, reference may be had to the following specification taken in con junction with the accompanying drawing, wherein:

FIG. 1 is a schematic illustration, partially in crosssection, of a trip device embodying one form of my invention.

FIG. 2 is a graphical representation of certain timecurrent characteristics of the trip device of FIG. 1.

FIG. 3 is a cross sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 shows a modified form of my invention.

Referring now to FIG. 1, there is shown a power -l-ine 10 having a circuit breaker 12 connected therein. The circuit breaker is schematically shown in its closed position where it is held against the bias of an opening spring 14 by means of trip latch 16. When the latch 16 is released, or tripped, the spring 14 responds by driving the circuit breaker open to interrupt the flow of current through power line 10.

For protecting electric apparatus connected to the power line 10 from overcurrents through the power line, it is customary to provide the circuit breaker with a trip device that can cause the circuit breaker to open with a time delay that varies in duration inversely with respect to the magnitude of the overcurrent. As pointed out hereinabove, a commonly used time current characteristic is one in which the time delay is made to vary inversely with respect to the current squared, i.e., t=K/I Such a time current characteristic is shown by curve A of FIG. 2.

In FIG. 1, I have shown a trip device 19 which is capable of operating in accordance with the desired time current characteristic. This trip device 19 comprises an electromagnetic pump 20 that is energized by currents supplied from the power line 10 through a current transformer 21. The current transformer 21 supplies a current to the pump that is directly proportional to line current except at the very high values of line current. The electromagnetic pump 20, when sufiiciently energized, pumps a conductive liquid 23, preferably mercury, through a conduit 22 into a tripping chamber 24. The tripping chamber 24 contains a piston-like actuator 26 that moves upwardly in response to the reception of liquid through the conduit to actuate a linkage 28. The linkage 28 responds by releasing the trip latch 16 to permit the circuit breaker 12 to open under the bias of its opening spring 14.

The electromagnetic pump 20 comprises a magnetizable core 30 of a generally C-shape and a coil 32 surrounding one of its legs. This coil 32 is connected in series with the secondary winding of the current transformer 21 so that it is energized by current approximately proportional to the current in power line 10. When current flows in one direction through the power line 10, the flux created by such energization follows the path generally indicated by the dotted line arrows 34. On half cycles of opposite polarity, the flux is in an opposite direction to the arrows 34. There is a gap in one of the legs of the core through which a section of the conduit 22 extends. The flux following the path 34 traverses the gap in a direction perpendicular to the longitudinal axis of the conduit section within the gap. The section of conduit 22 within the gap is preferably of an insulating material and has a pair of spaced apart electrodes 36 and 37 disposed at its laterally-opposed sides so that current flowing between the electrodes will flow across the conductive liquid in a direction at right angles to the flux traversing the conduit. The electrodes 36 and 37 are connected in series with coil 32 so that the current flowing between the electrodes 36, 37 is also generally proportional to the current in power line 10.

- In an electromagnetic pump such as 20 liquid is pumped through the conduit 22 when electric current is conducted through the conductive liquid in a direction transverse to the magnetic field that traverses the liquid. Accordingly, the desired pumping action occurs when current flows between the electrodes 36 and 37 and the coil 32 is energized to create flux across the gap. The direction that liquid will be pumped through the conduit 22 at any given instant depends upon the direction of current flow between the electrodes 36, 37 and the direction of flux traversing the conduit at this instant. In the illustrated pump 20 the direction of current flow is so selected relative to the direction of flux that pumping is always in the direction indicated by arrows 40, i.e., toward the tripping chamber 24. The current flowing between the electrodes is in phase with the flux so that changes in the direction of current at the end of each half cycle are compensated for by corresponding changes in the direction of the flux. As a result, the pumping action continues in the direction of arrow 40 despite changes in the direction of the current flow between the electrodes 36 and 37.

The pressure developed by the pump is approximately proportional to the product of the flux traversing the conductive liquid 23 and the current flowing between the electrodes 36 and 37. Since both of these quantities are proportional to line current, it will be apparent that the pressure developed by the pump at its discharge end D is approximately proportional to the square of the line current.

The flow through the conduit 22 is controlled by a restriction 42 located between the pump 20 and the tripping chamber 24. This restriction 42 is so designed that the flow rate therethrough is approximately proportional to the pressure upstream therefrom. Accordingly, the flow rate through the restriction 42 is approximately proportional to the square of the current in power line 10.

The tripping actuator 26 that responds to a pressure build-up in the tripping chamber 24 comprises a flexible diaphragm 50 that seals the top end of the tripping chamber and a plunger 52 secured to this diaphragm 50. When the pressure in the tripping chamber builds up to a predetermined minimum level, it deflects the diaphragm upwardly, thus driving the plunger 52 upwardly.

For transmitting upward motion of the plunger 52 to the trip latch 16, the previously mentioned linkage 28 is provided. This linkage 28 comprises a main trip lever 54 pivotally mounted on a stationary pivot 56 and biased in a counterclockwise direction against a stop 58 by means of a reset spring 60. The reset spring 60 also acts as a biasing means for opposing motion of the tripping actuator 26 and determining the minimum pressure that the tripping actuator can move in response to. When the plunger 52 of the tripping actuator 26 moves upwardly, it drives this main tripping lever 54 clockwise about its pivot 56 against the reset spring 60. Such clockwise motion is used for controlling an intermediate tripping lever 62, which is biased in a clockwise direction about a stationary pivot 64 by a tension spring 65. The intermediate tripping lever 62 carries a roller 63 at its lower end that bears against the right hand end of lever 54. Normally this intermediate tripping lever 62 is prevented by the right hand end of main tripping lever 54 from moving in a clockwise direction about its pivot 64. But when the main tripping lever 54 is driven by the plunger 52 in a clockwise direction about its pivot 56, the lower end of the intermediate tripping lever 62 is freed, and the spring 65 rotates it clockwise. This causes its upper end to pivot the trip latch 16 counterclockwise about its pivot 66 to permit opening of the circuit breaker 12.

The time required for the tripping actuator 26 to trip the latch 16 will depend upon the net flow of conductive liquid into the tripping chamber 24. For controlling the net flow of liquid into the tripping chamber 24, I provide a timing chamber 70 that is also hydraulically connected to the discharge end of the conduit 22. This connection is preferably made by means of a substantially unrestricted pipe 72 that communicates at one end with the tripping chamber 24 and at its other end with the timing chamber 70. The presence of this unrestricted pipe 72 will result in the pressure in the timing chamber 70 equalling the pressure in the tripping chamber 24.

The timing chamber 70 contains a diaphragm 74 sealing its lower end and exposed to the pressure in the timing chamber 70. The diaphragm 74 is biased in an upward direction by means including a float 75 attached to the diaphragm. This float 75 is located in a biasing chamber 76 at the lower side of the diaphragm that is filled with the conductive liquid. The float 75 is of a material less dense than the conductive liquid, which is preferably mercury. So it will be apparent that the buoyancy of the float 75 in the liquid of chamber 76 will force the diaphragm 74 upwardly with a predetermined and substantially constant upward biasing force. The normal, or uppermost, position of the float 75 is determined by an abutment 77 attached to the float which normally abuts against the top wall of the timing chamber 70. The combination of the diaphragm 74 and the float 75 is referred to hereinafter as timing structure.

The upward biasing force on the diaphragm 74 is of such a value that the pressure required in the timing chamber 70 to force the float 75 downwardly is slightly less than the pressure required in the tripping chamber 24 to force the tripping actuator 26 upwardly. Accordingly, when the pump 20 develops a pressure downstream from the restriction 42 that is sufli-cient to force the float 75 downwardly, all of the flow through conduit 22 will initially be into the timing chamber 70. In moving downwardly, the float 75 increases the volumetric capacity of the timing chamber 70 and maintains the pressure in the timing chamber 70 and the tripping chamber 24 substantially constant and below a value that will move the tripping actuator 26 upwardly. The pressure in chambers 70 and 24 is maintained at this value until the float 75 engages a stop 78 positioned therebehind. When this occurs, no additional liquid can enter the chamber 70 and the pressure in chambers 24 and 70 begins increasing, soon reaching a high enough value to drive the tripping actuator 26 upwardly to trip the circuit breaker. After the float has engaged stop 78, it will be apparent that all of the flow through conduit 22 is into the tripping chamber 24 instead of the timing chamber 70.

The stop 78 for the float 75 is an adjustable stop that can be adjusted to control the spacing 80 between the stop and the float when the float is in its normal position of FIG. 1. The time required for the pump to trip the circuit breaker varies as a direct function of the spacing 80. Hence, by increasing the spacing, the time required for tripping the breaker can be lengthened and by shortening the spacing, the time can be shortened.

Preferably the stop 78 is in the form of a rotatable cam fixed to a shaft 81 that is rotatably mounted in the bottom wall of the housing for the biasing chamber 76. By rotating the shaft 81 through an externally mounted dial 82 the position of the uppermost surface of the cam 78 can be altered to change the spacing 80. Suitable indicia is provided adjacent the dial 82 to provide an indication of the amount of spacing 80 that is present for any given adjustment of the dial 82. This indicia is preferably calibrated in terms of time to produce tripping at a given current level.

In FIG. 2 a typical time-current characteristic curve is shown at A for a trip device such as shown in FIG. 1. The approximate time required for the trip device to trip the circuit breaker is plotted as the ordinate against the current in power line expressed in percentage of pickup plotted as the abscissa. Both of these quantities are plotted on logarithmic scales. The term pick-up denotes the minimum value of current in the power line that will cause the actuator 26 to trip the circuit breaker.

When the stop 78 is rotated to lengthen the spacing 80, the characteristic curve will be shifted upwardly as shown for example at B to provide longer time delays, but the shape of the curve will remain substantially unchanged. Also there will be no substantial shifting of the curve horizontally so that the pick-up current will remain substantially unchanged. Conversely, when stop 78 is rotated to shorten the spacing 80, the characteristic curve will be shifted downwardly, as shown for example, at C, to provide shorter time delays but without substantially changing the shape of the curve or shifting it horizontally. It is highly desirable that these adjustments can be made without changing the shape of the curve or shifting it horizontally since this permits the times involved to be changed with a minimum of interference with system coordination.

The total time required for the actuator 26 to trip the circuit breaker will be the sum of the time required to drive the float 75 downwardly against its stop 78 and the time required to drive the actuator 26 upwardlysufliciently to release the trip latch 16. Each of these periods of time is directly proportional to the rate at which a net flow of fluid enters the particular chamber 70 or 24 involved. Since the net flow of fluid into each of these chambers is inversely proportional to the square of the current in the power line 10, the total time to trip the circuit breaker will also be inversely proportional to approximately the square of this current. The adjustment of stop 78 to change the time required for the float 75 to reach the stop 78 does not change this relationship. The total time to trip is still the sum of two quantities that are inversely proportional to approximately the square of the line current.

A feature that contributes to the ability of the trip device to maintain its characteristic time-current curve intact despite adjustments in the position of stop 78 is the location of the timing chamber 70 downstream from the restriction 42. If it were located upstream from this restriction, then changes in the position of stop 78 would change the shape of the characteristic time-current curve. Also a much larger volumetric capacity would be needed than in the arrangement of FIG. 1 in order to provide a given time delay.

A particular advantage of my adjusting means is that the time of response of the trip device is linearly related to the travel of the timing structure 74, 75 and can therefore be linearly related to displacement of the adjusting shaft 81. Thus, operation of the time-adjusting shaft 81 can produce adjustments in the time of response with the same high degree of precision over the entire time scale. There are no portions of the scale that are unduly senof the hydraulic system.

6 sitive or critical to operations of the time-adjusting shaft 81.

Although I prefer that the time for tripping be inversely proportional to approximately the square of the current, the invention is equally applicable to tripping arrangements that have other time-current characteristics, such a might be obtained, for example, by changing the length or cross-section of fiow restriction 42. In such arrangements, as in FIG. 1, adjustments of stop 78 will shift the characteristic time-current curve vertically without changing its shape or without shifting it horizontally (assuming such curve is plotted on the coordinates shown in FIG. 2).

It is to be understood that at currents below pickup, the pump 28 develops insufiicient pressure to displace either the float 75 or the actuator 26 from their respective normal positions shown in FIG. 1. Hence, the trip device 19, in effect, does not respond to these currents.

The trip device of FIG. 1 is a completely sealed system that is free of air or other gas pockets contacting the conductive liquid. In this respect, space 89 above the diaphragm 50 of the tripping chamber and the space 76 below the diaphragm 74 of the timing chamber are completely filled with the conductive liquid. A substantially unrestricted pipe 90 affords communication between these spaces 89 and 76 and also connects these spaces to the inlet end of the pump 20. A substantially unrestricted passageway 92 interconnects space 76 and the pipe 90. The spaces 89 and 76, in effect, provide a reservoir for the conductive liquid that the pump 20 forces through the conduit 22.

To prevent leakage about any of the moving parts that extend from the hydraulic system int-o the surrounding atmosphere, suitable seals are provided about these parts. For example, a suitable flexible boot 92 is provided about the main tripping lever 54 and an O-ring seal 93 is provided about the stop adjusting shaft 81.

It is to be noted that the two movable parts 54 and 81 projecting into the hydraulic system from the external surrounding space are rotatably mounted so that their motion doe-s not substantially change the effective volume In a sealed, completely-filled system such as shown, this is highly desirable because a change in the system volume can affect the pressure prevailing in the system or can lead to the creation of gas pocket-s. These conditions Will detract from the preciseness with which the system can produce tripping in accordance with predetermined operating characteristics.

Since the system is maintained free of gas pockets, the biasing chamber 76 beneath the float 75 will be maintained full of the conductive liquid. Hence, the upward force produced by the buoyancy of the float 75 will be maintained substantially constant. This same upward force will be present irrespective of the instantaneous position occupied by the float since the buoyancy of the float is not dependent upon its position so long as the chamber 76 is full. As contrasted to the bias that would be provided by an ordinary compression spring, there is no force gradient to cause the biasing force to increase as the spring-biased part compresses the spring. Hence, the timing float can yield to maintain the pressure in chambers 24 and 70 constant Without increasing this pressure. This makes it possible to set the respective motion-initiating pressures for the float 75 and the tripping actuator 26 closer together than would otherwise be the case.

In some circuit applications it is desirable that the tripping actuator respond to very high overcurrents in much shorter times than would be the case if the time varied inversely with the square of the current. If such high speed response at high overcurrents is desired, it can be obtained by introducing a suitable restriction 92a into the passageway 92, as shown in FIG. 4. In this modified form of the invention, this restriction 92a is made large enough to permit the float 75 during low and moderate overcurrents to be driven downwardly without increasing the pressure in biasing chamber 76. But when a very high overcurrent occurs, the float 75 is driven downwardly with such force that liquid cannot escape from the biasing chamber 76 fast enough to prevent a pressure build-up in the biasing chamber 76. This pressure build-up in biasing chamber 76 results in a pressure build-up in chambers 70 and 24, thus causing an immediate rapid upward motion of the tripping actuators 26 to trip the circuit breaker latch.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A current-sensing trip device for an electric circuit breaker comprising:

(a) a conduit containing an electrically conductive liquid,

(b) means including an electromagnetic pump for pumping liquid through said conduit at a flow rate varying as a function of the current flowing through an electric circuit,

(c) a tripping chamber hydraulically connected to such conduit for receiving liquid pumped therethrough,

(d) a tripping actuator exposed to the liquid in said tripping chamber and movable in a direction to trip said circuit breaker when the pressure in said tripping chamber exceeds a predetermined minimum value,

(e) first biasing means for opposing motion of said tripping actuator in a tripping direction,

(f) a timing chamber hydraulically connected to said conduit so as to receive liquid force through said conduit by said pump,

(g) timing structure exposed to the liquid in said timing chamber and movable to increase the volumetric capacity of said timing chamber when the pressure of the liquid therein exceeds a predetermined minimum value,

(h) second biasing means for opposing motion of said timing structure in a direction to increase said volumetric capacity,

(i) said second biasing means permitting said timing structure to move at a lower minimum pressure than the minimum pressure required to move said tripping actuator, so that liquid forced through aid conduit causes motion of said timing structure before causing motion of said tripping actuator,

(j) and stop means for blocking motion of said timing structure after a predetermined amount of timing structure motion, thereafter allowing said tr1pping actuator to move.

2. The trip device of claim 1 in combination with means for adjusting the position of said stop to control the travel of said timing structure before motion thereof is blocked, whereby to adjust the length of time before said tripping actuator can begin moving in a direction to trip said circuit breaker.

3. A current-sensing trip device for an electric c1rcu1t breaker comprising:

(a) a conduit containing an electrically conductive liquid,

(b) means including an electromagnetic pump for pumping liquid through said conduit at a flow rate varying as a function of the current flowing through an electric circuit,

() a tripping chamber hydraulically connected to such conduit for receiving liquid pumped therethrough,

(d) a tripping actuator exposed to the liquid in said 8 tripping chamber and movable in a direction to trip said circuit breaker when the pressure in said tripping chamber exceeds a predetermined minimum value,

(e) a timing chamber hydraulically connected to said conduit so as to receive liquid forced through said conduit by said pump,

(f) timing structure exposed to the liquid in said timing chamber and movable to increase the volumetric capacity of said timing chamber when the pressure of the liquid therein exceeds a predetermined minimum value,

(g) stop means for blocking motion of said movable timing structure after a predetermined movement thereof in a direction to increase said available volume,

(h) means for causing the liquid forced through said conduit by said pump to first drive the timing structure against its stop and to then actuate the tripping actuator.

4. A current sensing trip device for an electric circuit breaker comprising,

(a) a conduit containing an electrically conductive liquid,

(b) means including an electromagnetic pump and a restriction in said conduit downstream from said pump for causing liquid to flow through said conduit at a flow rate varying as a function of current flowing through an electric circuit,

(0) a tripping chamber connected to said conduit downstream from said restriction for receiving liquid flowing through said conduit and restriction,

(d) a tripping actuator exposed to the liquid in said tripping chamber and movable in a direction to trip said circuit breaker when the pressure in said tripping chamber exceeds a predetermined minimum value,

(c) first biasing means for opposing motion of said tripping actuator in a tripping direction,

(g) timing structure exposed to the liquid in said timing chamber and movable to increase the volumetric capacity of said timing chamber when the pressure of the liquid therein exceeds a predetermined minimum value,

(h) second biasing means for opposing motion of said timing structure in a direction to increase said volumetric capacity,

(i) said second biasing means permitting said timing structure to move at a lower minimum pressure than the minimum pressure required to move said tripping actuator so that liquid flowing through said restriction causes motion of said timing structure before causing motion of said tripping actuator,

(j) and stop means for blocking motion of said timing structure after a predetermined amount of timing structure motion, thereafter allowing said tripping actuator to move.

5. The trip device of claim 4 in combination with means for adjusting the amount of timing structure motion that can occur before said stop means is effective to block and motion, thereby to adjust the length of time before said tripping actuator can begin moving in a direction to trip said circuit breaker.

6. The current sensing trip device of claim 1 in which:

(a) said second biasing means comprises a biasing chamber filled with conductive liquid, and

(b) said timing structure comprises a part located in said biasing chamber and floating on said conductive liquid so that its buoyancy provides opposition to motion of said timing structure.

7. A trip device as defined in claim 1 and further comprising:

(a) a biasing chamber into which said timing structure moves while increasingthe volumetric capacity of said timing chamber,

(b) liquid in said biasing chamber that is displaced therefrom as said timing structure moves to increase the volumetric capacity of said timing chamber,

() a restricted passageway through which said displaced liquid leaves said biasing chamber,

((1) said restricted passageway being large enough to permit said timing structure to move fast enough to maintain the pressure in said timing chamber at a constant value during movement in response to relatively low overcurrents,

(c) said restricted passageway being so small that flow therethrough is so impeded during relatively high overcurrents that said timing structure is so retarded that a high pressure buildup occurs in said timing chamber and said tripping chamber before said timing structure encounters said stop.

8. A trip device as defined in claim 1 and further comprising:

(a) a biasing chamber into which said timing structure moves while increasing the volumetric capacity of said timing chamber,

(b) liquid in said biasing chamber that is displaced therefrom as said timing structure moves to increase the volumetric capacity of said timing chamber,

(c) a substantially unrestricted passageway through which said displaced liquid leaves said biasing chamber.

9. A trip device as defined in claim 1 and further comprising:

(a) a biasing chamber into which said timing structure moves While increasing the volumetric capacity of said timing chamber,

(b) liquid in said biasing chamber that is displaced therefrom as said timing structure moves to increase the volumetric capacity of said timing chamber,

(c) means for developing during high overcurrents a high enough pressure in said tripping chamber to move said tripping actuator before said timing structure can reach said stop,

(d) said latter means comprising a restricted passageway through Which said displaced liquid leaves said biasing chamber,

(e) said restricted passageway being large enough to permit said timing structure to reach said stop before the pressure developed in said tripping chamber during low overcurrents becomes high enough to move said tripping actuator.

10. The trip device of claim 1 in combination with means for adjusting the amount of timing-structure motion that can occur before said stop means is efiective to block said motion, whereby to adjust the length of time before said tripping actuator can begin moving in a direction to trip said circuit breaker.

11. A current-sensing trip device for an electric circuit breaker comprising:

(a) a conduit containing an electrically conductive liquid,

(b) means including an electromagnetic pump for pumping liquid through said conduit at a flow rate varying as a function of the current flowing through an electric circuit,

(c) a tripping chamber hydraulically connected to said conduit for receiving liquid pumped therethrough, (d) a tripping actuator exposed to the liquid in said tripping chamber and movable in a direction to trip said circuit breaker when the pressure in said tripping chamber exceeds a predetermined minimum value,

(c) means for adjusting the time required for said tripping actuator to trip said circuit breaker comprising a movable part projecting into the liquid of said tripping device -from the region outside said liquid,

( f) said movable part being so mounted that its movement does not change the effective volume of said trip device containing said conductive liquid.

12. A current-sensing trip device for an electric circuit breaker comprising:

(a) a conduit containing an electrically conductive liquid,

(b) means including an electromagnetic pump for pumping liquid through said conduit at a flow rate varying as a function of the current flowing through an electric circuit,

(c) a tripping chamber hydraulically connected to such conduit for receiving liquid pumped therethrough,

(d) a tripping actuator exposed to the liquid in said tripping chamber and movable in a direction to trip said circuit breaker when the pressure in said tripping chamber exceeds a predetermined minimum value,

(c) movable structure projecting into the liquid of said trip device from the region outside said liquid,

( f) all of said movable structure that projects into the liquid of said tripping device from the region outside the liquid being so mounted that motion thereof does not change the efiective volume of said trip device containing conductive liquid.

References Cited by the Examiner UNITED STATES PATENTS 1,747,044 2/1930 =Bainbridge 317-36 1,773,036 8/1930 Fitzgerald 317--157 2,859,303 11/ 1958 Anderson 2001 12 2,944,127 7/ 1960 Carlson 200-412 BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, JR., Assistant Examiner. 

12. A CURRENT-SENSING TRIP DEVICE FOR AN ELECTRIC CIRCUIT BREAKER COMPRISING: (A) A CONDUIT CONTAINING AN ELECTRICALLY CONDUCTIVE LIQUID, (B) MEANS INCLUDING AN ELECTROMAGNETIC PUMP FOR PUMPING LIQUID THROUGH SAID CONDUIT AT A FLOW RATE VARYING AS A FUNCTION OF THE CURRENT FLOWING THROUGH AN ELECTRIC CIRCUIT, (C) A TRIPPING CHAMBER HYDRAULICALLY CONNECTED TO SUCH CONDUIT FOR RECEIVING LIQUID PUMPED THERETHROUGH, (D) A TRIPPING ACTUATOR EXPOSED TO THE LIQUID IN SAID TRIPPING CHAMBER AND MOVABLE IN A DIRECTION TO TRIP SAID CIRCUIT BREAKER WHEN THE PRESSURE IN SAID TRIPPING CHAMBER EXCEEDS A PREDETERMINED MINIMUM VALUE, (E) MOVABLE STRUCTURE PROJECTING INTO THE LIQUID OF SAID TRIP DEVICE FROM THE REGION OUTSIDE SAID LIQUID, (F) ALL OF SAID MOVABLE STRUCTURE THAT PROJECTS INTO THE LIQUID OF SAID TRIPPING DEVICE FROM THE REGION OUTSIDE THE LIQUID BEING SO MOUNTED THAT MOTION THEREOF DOES NOT CHANGE THE EFFECTIVE VOLUME OF SAID STRIP DEVICE CONTAINING CONDUCTIVE LIQUID. 